Process for refining lead or lead alloys



Dec. 19, 1944.,

Filed March 19, 1942 RECOVERY OF BISMUTH FROM THE CAUSTIC SODA SLAG M PU RE BL-PbALLOY Nd "515M UTH REMOVING POT MOLTEN CAUSTIC SODA I -(A) SLAG CONTAINING BIS- OR (B) MUTH AND SODIUM BL-FREE LEAD Y I I CONTAINING Na.

, LEACHING WATER CAUSTIC SODA I soLuTIoN TREATMENT T0 F'LTER REMOVE Na FUSED BISMUTH CAUSTIC DA 50 POWDER DE'BISMUTHIZED LEAD FREE OF SODIUM E 2 COKE SAND BATCH OR CONTINUOUS RECOVERY or BQMUTH mom THE CAUSTICSQM I i FURNACE IMPURE B1. Pb WW Mil/I6 BIZ-PI, ALLOY boLLscrIusAuoi 'gflg'gggflg" I i mm W cnuggasgwn DISMUTH aIsMu H 25 2 REMOVING POT couzcrma P01 1 l HYDROGEN HIGH CONTENT Dl-BISMUTHIZED 51: FREE LEAD B|$MU1H- LEAD causncsomsm CONTAINING Na. ALLOY aoN) PW i I TREATMENT TO i Rsmovguas I I J0 STPH CDITIMFR 4 INVENTOR. DEBIJMUTNIZED I LEAD I CRUDE FREE OF somun BI' 5MU |H alloys.

' Patented Dec. 19, 1944 Joseph C. Dittmer, St. Albans, N. Y., assignor to National Lead Company, New York, N. Y., a corporation of New Jersey Application March 19, 1942, Serial No. 435,294 (Cl. -75'78) 12 Claims.

The present invention relates to the refining; of

lead and lead alloys. More particularly it relates to a process for the refining of lead or lead alloys by the removal of the bismuth contained therein to any extent desired up to the total bismuth content, and more selectively than by methods heretofore used.

It is known that bismuth may be removed from lead or lead alloys by the use of alkali and alkaline earth metals, which react with the bismuth to form intermetallic compounds having higher melting points than the base metal treated. However, such methods of removal have not been wholly satisfactory since, because of the solubility of the bismuthide inthe base metal, it has notbeen possible to obtain a substantially-complete removal of the Furthermore, the intermetallic compounds formed in such removal processes are contained in a wet metallic mush or dross which is largely composed of thebase metal, i. e., the lead or'lead alloy, treated.

Hence, various drying methods have been suggested in order to reduce the quantity of base metal held by the Wet mush. However, in spite bismuth from the lead or lead stirring the metal/gradually adding an alkali,'

dross Which'is a considerable proportion ofthe metal treated and which is uneconomical to re-- work; and recovering the bismuth which has been removed fromthe base metal. Further objects will become apparent as the descriptionof my invention proceeds. J

My invention contemplates treating in a molten condition the lead or lead alloy containing bismuth with one or more of the alkali or alkaline earth metals, thereby to form a bismuthide. This reaction is carried out'in the presence of-a flux.

of caustic soda. Thus, I have found that by covering the molten bismuth containing base metal with a molten flux of caustic soda which will dissolve the bismuthide, and, while preferably alkaline earth intermetallic reagent such as metal- He sodium, while maintaining the temperature of these drying treatments, considerable base metal is still held by the dry dross.

The prior art has also suggested subsequent treatments of the wet dross by'various operations or combinations of operations involving pressing, liquating, and leaching in acid solutions or in molten baths-of fluxes for the purpose of lowering the lead base metal content of the dross. However, considerable lead base metal still remains and subsequent smelting or refining operations are necessary to recover these metal values.

Another recommendation of the prior art is to preferably as close to the meltingpoint of the metal as practical operation will'permit, the bis muth can be substantially completely and selectively removedfrom the lead or lead alloy base metal, and in one operation if desired. While it is preferable, in order to insure a substantially complete removal of the bismuth, to employ an amount of the alkali or alkaline earth metal reagent in excess of theoreticalstoichiometric requirements, just sufiicient amounts of flux and intermetallic reagent may be added to efiect the removal of the bismuth to the desired extent, and

. these'amounts will depend upon the'quantity of bismuth to be removed, and the desired complete- ,1 ness of the removal.

treat the dross containing bismuthides with Water or dilute acid solutions so as to decompose the bismuthides and liberate bismuth which, it is claimed, can then be separated from the bulk of lead base metal by some form of classification. However, these treatments involve extraoperations, the handling of large amounts of drosses, and the reclaiming and retreatment, with attendant losses, of a considerable amount of lead base metal associated with the bismuthides in the dross, which dross may amount to about 10% or more of the original metal treated.

Objects of the present invention include overcoming the disadvantages described above; obtaining a substantially complete, selective and inexpensive removal of bismuth from lead or lead alloys; preventing the formation of a large metal It has been found that the last traces of bismuth are much more diflicult to remove and therefore require relatively larger proportions f flux and reagent.

For example, in removingsubstantially all the bismuth from a lead alloy containing about 0.1%

bismuth, sufiicient metallic sodium was used to bring the sodium content of the metal to about 4%' Na. Only enough caustic soda to dissolve the sodium bismuthide and still maintain the slag sufficiently 'fiuid would be necessary, but it is usually advantageous to use more in order to keep the surface of the metal covered to prevent its oxidation. The caustic soda also prevents the oxidation of metallic sodium durin its addition.

The sodium can be introduced in solid form into the molten metal under treatment either as metallic sodium or as a high percentage sodium alloy .by methodswell known to those experienced in the art. Thus, bricks of metallic sodium can be cut up into small pieces and rapidly projected in any suitable way into the vortex of the vigorously stirred base metal or, because of-the lightness size nozzle and pipe directly "for each treatment.

of metallic sodium, the sodium can be cut or otherwise formed into small pieces or particles, then mixed with the desired proportion of powdered lead, pressed into the proper sized briquet and this briquet fed into the vigorously stirred base metal. Alternatively, the sodium or sodium. alloy, in an atmosphere of dry nitrogen gas, can be melted in a suitable container and fed through a proper into the rapidly stirred base metal.

The sodium in whatever form or way it is introduced, reacts with the bismuth contained in the lead or lead alloy forming sodium bismuthide. I have found that a relatively large excess of sodium decreases the solubility of the bismuthide in the base metal. Simultaneously, the bismuthide selectively dissolves in the molten caustic soda flux, the solubility in the flux increasing cor.-

respondingly as the solubility in the metal is decreased by the addition of the excess sodium to the metal. Thus, a very selective separation of the bismuthide from the base metal is obtained.

As an illustration of the results to be accomplished by my invention, the following example is given:

Example No. 1

Original metal treated: 9084 grams of an 0.109% Bi-Pb alloy.

Metal covered with molten causticsoda and stirred.

Metallic sodium added: 500 grams.

Average temperature: 342 C.

A comparison of the above data of Example No. 1 with that given below in Example No. 2 for a bismuth removal using four treatments with caustic soda instead of the one used in Example No. 1 shows that one treatmentis sufficient to give a satisfactory removal of the bismuth.

Example No.2

Original metal treated:- 9072 g. of an=0.109% Bi-Pb alloy. T

Metal covered with 4' succe molten caustic soda.

Metal and'caustic soda were stirred one hour ssive batches of 500 grams sodium: added in 4 equal portions of 125 g. each.

Average temperature: 347' C.

If desired, sodium chloride and sodium carthe bismuth removal from alloys of correspondingly low melting points.

I have found that temperatures between 'just above th melting points of the metal treated and the flux used and below 350 C. give the most satisfactory removals of bismuth. In the removal of bismuth from lead, temperatures of 340 to 350 C. are the most satisfactory for practical operation.

If desired, the slag containing the bismuthide can be skimmed off in any suitable way and leached with water to dissolve the caustic soda and break up the sodium bismuthide into sodium hydroxide and bismuth, the latter being recovered by filtration and'other operations well known to those experienced in the art. According to my U. S. Patent No. 1,976,333, the resulting solution of caustic soda can be used for the complete I'E-f moval of the residual sodium left in the base metal after the removal of the bismuth and can thus be simultaneously concentrated back again into molten caustic soda for use in the subsequent bismuth-removal treatment of other batches of bismuth-containing lead or lead alloys. duced into the vortex of the vigorously stirred molten base metal gives up its moisture to act on the sodium contained therein and thus converts it into sodium hydroxide.

The bismuth can also be recovered from the caustic soda slag by'adding silica, sand or' other neutralizing materials and smelting, but this is undesirable and uneconomic.

The recovery of bismuth from the caustic soda slag by either leaching or smelting in the manner above described is illustrated in the accompanying flow sheet designated as Fig. 1.

Instead of the above methods, the bismuth contained in the molten caustic soda slag' can be reclaimed by concentrating it in another metal. Thus, I have found that when the molten caustic soda slag containing the bismuth is vigorously stirred in contact with a molten lead or lead alloy containing little or no sodium, all the bismuth can be dissolved out of the slag and goes into the lead or lead alloy. For example, 8788 grams of a lead alloy containing 0.12% bismuth and 001.6% sodium was stirred for about an hour at 340 to 370 C. with 2331 grams of caustic soda slag containing 0.155% bismuth and 0.08% lead. After treatment, the slag contained 0.03% lead but no bismuth, and th alloy analyzed 0.157% Bi and 0.006% Na. Most of the sodium in the slag is oxidized during the treatment and therefore only some of it enters the alloy. As sodium retards the extraction by the alloy of the his muth in the slag, it is desirable to remove the sodium fromthe alloy by using either a. solution of caustic soda as described above or-. by

bonate may be added to the caustic soda flux in blowing steam into the vortex -of the stirred massof metal and slag during the bismuth extractiontreatment. Other methods of oxidizing the sodium can be employed such as by blowing air into the metal and. slag or by adding an oxidizing reagent such as lead oxide.

I have further. found that the recovery of the bismuth by the process as desbribed in the preceding paragraphcan be combined with the bismuth-removal process and thus effect economies in the use of metallic sodium and caustic soda by the simultaneous and continuousoperation of both processes as follows: The molten caustic soda slag in the" bismuth removal" pot is.

The solution of caustic soda when introdroxide.

which is preferably at a somewhat higher level and from which the slag can flow by gravity through an overflow pipe back into the bismuthremoval pot. The caustic soda slag and bismuthcollecting metal are preferably vigorously stirred v in contact toefiect the more'rapid and eflicient I solution of the bismuth. The vigorous stirring,

or lead alloys which omprises' melting the metal to be pu ified, covering the v:same with a flux of molten caustic soda, admixing therewith an amount of metallic sodium in excess (if-normal a melting'point of the mass and not in excess of also causes some oxidation of the sodium taken p by the metal, whichis desirable.

The aforementioned batch or continuous method for recovering the bismuth fromithe molten caustic slag by concentrating the bismuth in a molten lead or lead alloy is illustrated in the accompanying flow sheet designated as Fig. 2.

- It is to be understood thatthe i'oregoing de scription and examples'of my invention have been given, merely for illustrative and not limitative purposes. Therefore, it will be appreciatedthat there is no intention of excluding from the scope 2. A process for removing bismuth from lead or lead alloys which comprises melting the metalstoichiometric requirements, and agitating the mass at a temperature which is just above the about 350 C.', uhtil the desired removal of the bismuth is' effected.

8. Aprocess for removing bismuth-from lead. or lead alloys which comprises melting the metal to be purified, admixing therewith in the presence of axmolten caustic soda fiux, at least one or the metalsfrom the group consisting of the alkali f and alkaline earth metals, thereby to form a bismuthide, skimming oil the bismuthide-containing slag formed, leaching the same with water and recovering therefrom the bismuth values; 9. A process for removing bismuth fro'm lead Or lead alloys whichcomprises melting the metal 1 to be purified, admixing therewith metallic so- A dium pieces in the presence of a molten flux of water, thereby to form bismuth and a causticrsoda or lead alloys which comprises melting the metal caustic soda, thereby to'form sodium bisinuthide,

skimmingofi. the resulting slag containing the sodium -bismuthicie, leaching the said .slag with solution, recovering the bismuth and employing the caustic soda solution-to remove the residual sodium which may be present in the refined metal by virtue of the bismuth removal process;

10. A process for removing bismuth from lead to be purified, and while vigorously stirring. the

same, admixing therewith in the presence of a vto be' urified and while vigorously stirring the flux of-molten caustic soda at least one of the same, admixing therewith at least one or the metals from the group consisting of the alkali and alkaline earth metals, thereby to form a bismuthide, said reaction being carriedout in the presence of a flux containing essentially and pre metals from the group consisting of the alkali and alkaline earth metals, thereby to form abismuthide, skimming ;off the resulting bismuthide dominantly caustic soda, which said fiux is devoid of potassium hydroxide. 3. A process for removing bismuth from lead "or lead alloys which comprises melting the metal to be purified, and while vigorously stirring the same, admixing therewith at least one :or the metals from the group consisting of the'alkali j and alkaline earth metals, thereby to form 9. bismuthide, said reaction being carried out in the presence of a flux containing essentially and predominantly. caustic soda, with optional minor amounts or sodium chloride and carbonate, which said fiux is devoid of potassium hy- '4..A process for removing bismuth from lead or lead alloys which comprises melting the metalto be purified, and while vigorously stirring the bismuthide, said reaction being carried out in the presence-0f a flux-oi caustic soda. 5. A process, for removing bismuth from lead a or lead alloys which comprises melting the metal.

-'to be purified, covering the same with a flux of;

=molten caustic soda, and admixing therewithme- :tallic sodium until. the

.-bismuthisefiected.- g- Y 6. A process-for removing bismuth from lzad desired removalof the .or lead alloys which comprises melting the m to be purified, covering the same with a flux of molten caustic soda, admixing therewith metallic sodium, and repeating the additions :of flux and- \..1netallicscdium until the bismuth is 'substan tially completely removed.

'7. A process for removing. bismuth from containing caustic soda slag, stirring the said slag in molten conditionwith a relatively smallamount of molten lead or lead alloy, substantially free of sodium, until the bismuth-values are dis,

solved therein.

11. 'A continuous process for-removing bismuth from lead or lead alloys which comprises melting the. metal to be purified, and while vigorously stirring the same, admixing therewith in the presence of a fiux of molten caustic soda, at least of the resulting molten-bismuthide-containing.

' same, admixing therewith sodium to form sodium one of the metals'from the group consisting of the alkali and alkaline earth metals, thereby to.

form a bismuthide, continuously removing apart caustic soda slag, stirring the said slag in contact with a-relatively small amount of molten lead or lead alloy until the bismuth values are substantially dissolved therein and returning the resultant molten caustic soda slag for further use in the bismuth-removal treatment.

12. A continuous process for removing'bismuth from lead or lead alloys which'comprises melting the metal to bepurified, and while vigorously stirring the same, admixing sodium therewith. in.

the presence of a flux of molten caustic soda,

. Josnrn c. nrrnma, 

